The present invention is directed generally to fasteners carrying captive members and more particularly to a terminal clamp assembly comprising a fastener and one or more captive members and a method for making such a terminal clamp assembly.
While the present invention is applicable to fasteners which carry captive members in general, the disclosure will be facilitated by specific reference to a terminal clamp assembly. Typically, such terminal clamp assemblies are utilized for removably securing the end or ends of one or more conductors to a work piece, such as a terminal block, bus bar, circuit breaker or the like.
Conventionally such terminal block assemblies include one or more surfaces which may be specially formed or otherwise adapted to receive at least one conductor element connected thereto by a terminal clamp. A suitable threaded aperture is generally provided in the conductor receiving surface for receiving a complementarily threaded shank portion of a terminal clamp fastener.
Accordingly, such terminal clamp fasteners conventionally include a fastener comprising a head portion and threaded shank portion and at least one clamping member carried on the fastener. Preferably, the clamping member is captively assembled with the fastener. To this end, such fasteners generally include an unthreaded shank portion of lesser diameter than the thread, intermediate the drive head and threaded shank portion for captively holding the clamping member, to provide a unitary terminal clamp fastener assembly. The problem, then, is in assembling these parts in this fashion.
Since such terminal clamp fastener assemblies must generally be provided in large quantities, it is important to minimize the cost of production and assembly thereof. In this regard, various economies have been introduced in the formation of threaded fasteners. However, there is room for yet further improvement.
The prior art has proposed a number of solutions to the problem of economically providing a pre-assembled fastener with captive clamping member. For example, the conventional Sems technique is disclosed in U.S. Pat. No. 3,191,140. In this regard the word "Sems" has been generally utilized in the art to refer to such fastener and captive member assemblies. In the aforementioned U.S. Pat., one or more captive clamping pieces or the like are preassembled to a fastener to screw blank, whereupon the thread is rolled or otherwise formed thereupon. However, the captive member must then undergo the same heat treatment as the fastener or screw, which has the disadvantage of depriving the captive member of its desired resiliency.
Lanius U.S. Pat. No. 3,238,495 proposed to avoid these problems by individually heat treating the already formed screw or fastener and other captive parts as desired, prior to assembly thereof. Accordingly, Lanius proposes first forming and heat treating a threaded screw or fastener, including a drive head, a thread portion of given crest diameter and an unthreaded shank portion intermediate the drive head and threaded shank portion and of lesser diameter than the thread crest diameter. Hence, the captive members to be assembled with this fastener include a through aperture of diameter at least as great as the thread crest diameter to interfit thereover for engagement with the drive head and generally surrounding the unthreaded shank portion. Accordingly, Lanius proposes staking at least the captive member farthest removed from the drive head to accomplish captive assembly thereof, and of any further captive members thereunder, with the fastener. In this regard, Lanius proposes staking by the expedient of pushing or deforming a portion of the lower surface of this captive member toward the unthreaded shank portion. However, the success of this technique in producing a reliable captive assembly depended upon the characteristics of the staked material (i.e. hardness, brittleness, resiliency, etc.), and upon the amount of material moved during the deformation or staking process. Moreover, such terminal clamp assemblies generally include a U-shaped bracket member, within which a second, wire clamping member is positioned. Accordingly, reliably staking the clamping member from the bottom within the confines of the U-shaped clamp member has proven difficult.